Table of Contents DVOM Subject Page DVOM.3 Introducing the DVOM .3 Choosing a DVOM.3 The Functions .5 Function Selector Rotary Switch .5 Push Button Functions .7 Input Terminals .9 Display.9 Infinity Display.10 Using the DVOM .11 Voltage Testing .11 Amperage Testing .12 Resistance Testing.13 Continuity Testing.14 Voltage Drop Testing .15 Worksheet Exercises.16 Worksheet 1 .16 Worksheet 2 .17 Testing Circuits .18 Circuit 1 .18 Circuit 2 .19 Circuit 3 .20 Circuit 4 .21 Initial Print Date: 12/04 Revision Date: 3/06 DVOM Model: All Production: All ■micmiis After completion of this module you will be able to: • Choose a proper multimeter for testing. • Correctly install a DVOM in a circuit for testing. • Understand the use of a DVOM for electrical testing of circuits. • Know how different types of circuits are tested. • Complete and understand the following tests as performed on circuit boards: - Voltage - Amperage - Ohms - Voltage Drop Test 2 DVOM DVOM Introducing the DVOM The ability to measure voltage, current flow, and resistance is important in the diagnosing of electrical problems. Without the results of these measurements troubleshooting in an electrical system is a futile process. The instrument most commonly used to make electrical measurements is called the Digital Voltage-Ohm Meter (DVOM). Basic DVOM’s are capable of measuring: • AC Voltage • DC Voltage • Millivolts • Resistance • Conductance • Capacitance • Continuity • Diode Test • Amps/Milliamps Advanced DVOM’s add: • Microamps • Frequency • RPM • Duty Cycle • Pulse Width The DVOM provides for a method of accurate measurements. Even though accurate measurements are the key to electrical diagnosis, the following four factors determine the effectiveness of the measurements: • Accuracy of the measuring instrument. • Correct installation in the circuit of the measuring instrument. • Ability of the Technician to read the instrument. • Skill of the Technician in interpreting the results. As it is clearly seen, only one of the factors depends on the DVOM (e.g. accuracy), the rest will always depend the ability of the technician to read and interpret the results. Choosing a DVOM A good choice of a DVOM is the DISplus or the GT1, as the measuring system of each contains a highly accurate DVOM. Choosing a handheld DVOM from a reputable manufacturer, however, leaves the DISplus and GT1 free to perform other tasks that a DVOM can not do (e.g. Retrieval of fault codes). 3 DVOM In choosing a DVOM several factors need to be considered, one of which is Impedance. Impedance is the combined resistance to current created by the resistance, capacitance and inductance of the meter. Impedance is measured in ‘Ohms per Volt’. Meters with the highest ‘Ohms per Volt’ impedance are the most accurate. More importantly using a meter with high impedance will not cause damage to sensitive electronic circuitry. When a Meter is connected across a circuit to measure voltage, it must be connected in parallel. This adds parallel resistance. The total resistance in a parallel circuit is less than the lowest resistance in that circuit (Ohms Law). Using a Meter with low impedance will reduce the total resistance of the circuit and allow more current to flow. A meter with low impedance can draw enough current to cause inaccurate measurement, voltage drops or damage sensitive electronic circuit boards. A high impedance meter will draw little current and insure accurate readings. Using older type meters with low impedance values (20,000 to 30,000 ohms-per-volt) can damage modern electronic circuits and components or give inaccurate readings. Test lights should be avoided for the same reason. They lower the total resistance of the circuit and cause increased current flow. Other factors in choosing the proper DVOM are: • Cost • Features Basic DVOM’s are available reasonably priced. These basic models may be more than sufficient for use in BMW Centers, given the availability of the DISplus and GT1 for advanced measurement and scope functions. Advanced features and price go hand in hand. The more features added the higher the cost. Some of those features may be worth the increase in cost (e.g. frequency, duty cycle and pulse width). Other features may not (e.g. oscilloscope, graphing). Choose a DVOM wisely based on personal preference and cost. Like many other tools it is valuable in the diagnosis and repair of BMW’s. Experience has shown if the technician is not comfortable with the DVOM or confident in the results of the measurements, the DVOM will not be used. Considering the technology in BMW automobiles, diagnosing with a quality DVOM cer¬ tainly makes repairing the problem correctly and expediently a more manageable task. 4 DVOM The Functions Function Selector Rotary Switch turned off. — mV "-^\-N- — v/ \ mA rpm/ mA I A 'v- offv JS Volts AC Measures AC Voltage Ranges: 400mV,4V,400V, 1000V Measures DC Voltage Measures DC Millivolts Ranges: 4V, 40V, 400V, 1000V Range: 400mV 5 DVOM Measures Continuity and Ohms. Test diode operation. Ranges: 400Q ,4kQ , 400kn , 4MQ, Range: 3.000V 40MQ Milliamp or Amps DC Measures DC Milliamps or amps. Measures AC Milliamp or amps Ranges: 40mA or 400mA for mA input Ranges: 40mA or 400mA for rmA input 4000mA or 10 A for A input 4000mA or 10 A for A input 6 DVOM Push Button Functions (zero A) JmIN MAX ^ RANGE^ | HOLD e) O i r RPM ^ DUTY^ ^LERTcX]) SMOOTH HZ ms-PULSE +TRIGGER Zero (Relative Reading) Function Displays difference between the measured value and the stored value. Minimum (Min), Maximum (Max), Average (AVG) Recording Records minimum, maximum and calculates the true aver¬ age. Manual Range or Auto Range In Manual Range user selects fixed range. Meter stays in that range until user changes it, selects Auto Range or turns meter off. In Auto Range meter selects range automatically. Touch Hold Touch Hold holds last stable reading on display. A new stable reading causes beeper to sound and display to update. If meter is in MIN MAX Recording, RPM, Duty Cycle, Pulse Width or Hz, Touch Hold interrupts the function. The display is frozen, but recorded readings are not erased. 7 DVOM RPM/HZ RPM 2, RPM 1, or frequency RPM 2, 4-cycle engines RPM 1, 2-cycle engines Hz. counts frequency between 0.5 Hz and 200 kHz. ms-PULSE Duty Cycle or Pulse Width Duty Cycle between 0.0 and 99.9% displayed. Pulse Width between 0.002 and 1999.9 ms displayed. t TRIGGER Change Alert, Continuity Beeper or +/- Trigger. In voltage or current functions selects Change Alert. In W function selects Continuity Tests. In Duty Cycle or Pulse Width selects trigger slope. O SMOOTH V- Smoothing Function and Back-light display (advance model only). Smooth displays average of last eight readings. Press Yellow button to turn on or off back-light. 8 DVOM Input Terminals Display 9 DVOM Infinity Display While most displays of DVOMs are standard (i.e. mV means millivolt, mA means mil- liamp) the display or symbol for infinity or open circuit can be confusing. A display of OW indicates no or little resistance. It means the circuit or portion of the circuit being mea¬ sured has continuity or is complete. A reading of OL means the circuit is open or not complete, the resistance is said to be “INFINITY”. Some meters may use the symbol B for Infinity. Be aware of which reading the meter being used will give for infinity or open circuit. Meter 1 10 DVOM Using the DVOM Voltage Testing The voltmeter (DVOM) must be connected in parallel with the load or circuit. The DVOM has a high resistance and taps off a small amount of current. A voltmeter must be used with the current on and with the correct polarity. The red lead should be connected to the B+ side of the circuit and the black lead to the B- side of the circuit. If the leads are reversed the reading will be a negative number. • Select proper function and range of DVOM. • Connect (-) lead of meter to battery B- or known good ground. • Connect (+) lead of meter to test circuit. DVOM will indicate supply or available voltage at that point. Typical Application of Voltage Testing • Checking Power Supply. • Charging System. • Complete Basic Circuits. • Control Module Functions (Input/Output). Measure at different points checking for change or interruption in the voltage supply. 11 DVOM Amperage Testing To measure amperage the meter must be installed in series in the circuit. The current flow of the circuit must flow through the meter itself. Current must be flowing in the circuit. Installing the meter in parallel with the circuit may cause damage to the meter, because of the increased current flow in the circuit, due to the low resistance in the meter. Caution: Most ampere meters or DVOMs are rated for no more than 10 amps. Current flow above 10 amps will damage the internal fuse of the DVOM and render it unable to measure amperage. • Select proper function of DVOM and move leads to proper position. • Connect meter in series with (+) lead on the B + side of the circuit. • Connect (-) lead of meter to complete circuit. DVOM will indicate current flow (Amps) through circuit. Typical Application of Amperage Testing • Proper Component Operation (Correct Current Draw). • Parasitic Draw Testing. Ensure meter is capable of handling current flow. £ 12 DVOM Resistance Testing When set for resistance testing (Ohms) the DVOM must never be connected in a live circuit. The component or portion of a circuit being measured, must be isolated from the power source. Most modern day DVOM’s are self ranging when set to measure resistance, so the meter can not be damaged by out of range measurements. The test leads may be used without regard for polarity, unless the circuit contains a diode. The DVOM functions by placing a very small amount of current on the circuit being test¬ ed, the red lead must be placed on the anode side of the diode. • Select correct function and range (Most meters are self ranging in this function). • Disconnect power to circuit. • Disconnect any circuit wired in parallel with circuit being tested. • Connect test leads. DVOM will indicate resistance (Ohms) of component or circuit being tested. Continuity Testing The DVOM uses its own internal power supply to test the continuity of the circuit. The DVOM must never be connected in a live circuit. Any circuits wired in parallel with the cir¬ cuit being tested must also be disconnected. Continuity testing verifies that circuit connections are intact. The continuity mode is extremely fast and is used to detect either shorts or opens that last as little as 1 ms. When a change is detected the beeper tone is stretched to last at least 1/4 second so both shorts and opens can be audibly detected. This is a valuable troubleshooting aid when diagnosing intermittent faults associated with wiring, connections, switches and other components of the circuit. • Select correct function and range of DVOM. • Disconnect power to the circuit. • Disconnect any circuits wired in parallel. • Connect DVOM leads to the circuit to be tested. DVOM display will indicate continuity of circuit. 14 DVOM Voltage Drop Testing Voltage Drop Tests determine the resistance of an active circuit, a circuit with current flowing. Voltage drop tests are preferred over simple resistance measurements because the power source is not removed from the circuit. By measuring the voltage on both sides of a load, the amount of voltage consumed by the load is measured. The voltage drops of each part of a series circuit added together must equal the power supply for that circuit while it is active. • Select proper function and range of DVOM. • Connect (+) lead to the B+ side of the circuit or component being tested. • Connect (-) lead to the B- side of the circuit or component. DVOM display will indicate the voltage drop in the circuit tested between the DVOM leads. Typical Application of Voltage Drop Testing • Determine proper component operation. • Active circuit continuity • Active circuit resistance. As a “Dynamic” test with the circuit operational, a voltage drop in any non-resistive part of the circuit indicates a fault in the circuit. 15 DVOM Worksheet Exercises Worksheet 1 DVOM Worksheet 2 s ' AUTO RANGE RECORD MAX MIN AVG Q AC Dc\ □ ms % — m V A M K Q mil A Hz RPM ± < 0 12 3 4 .1. . i . .In.Ik 4000 IIIIIIIIIIIIIIIIMIMIIIIIIIMIIMMIIIIr ™v / ( zero A) ( min max ) ^ RANGE^ ( hOLD e) ^ RPM ^ (% DUTY^ (ALERT gj) SMOOTH HZ ms-PULSE + TRIGGER — mV s— M- — v/ \ mA RPM / J\ A — 'v, V \ / mA / A ^ 400mA MAX | Fused -1000 V MAX- I Tip on Using a DVOM Inspect test leads and replace damaged leads. Do not use a meter if it looks dam¬ aged. Select the proper range and func¬ tion for your test. Disconnect the live test lead before disconnecting the common lead. When measuring current, turn the power off in the circuit before con¬ necting the meter. Check meter fuse(s). Note: Some meters may have leads and functions in different locations. Explanation of features can be obtained in their Users Manual. 17 DVOM Testing Circuits Circuit 1 Build this circuit per Wiring diagram. Use one bulb initially, second bulb will be added. Do not turn on power supply until instructed. Before applying power check voltage of power supply. • Measure resistance of one bulb. _ • Turn on power supply. Measure voltage drop across entire circuit. _ • Measure voltage drop across bulb._ • Measure amperage of the circuit. _ • Measure the resistance across a second bulb. Hot All Times • Install the second bulb. Measure amperage of the circuit. • How did the amperage change? Why? • Measure the voltage drop across each bulb. • Check voltage drop across top of fuse. • Remove fuse and check voltage drop across fuse terminals. • What type of circuit is this? _ STOP DO NOT DISASSEMBLE CIRCUIT Completed circuit should look similar to this. 18 DVOM Hot All Times Circuit 2 Build this circuit using the Wiring diagram. Be sure the power is OFF. • What should the voltage be at points 1 and 2 ? (Do not measure) _ • What should the voltage be at points 3 and 4 ? (Do not measure) _ • Turn on the power supply. Measure the voltage at point 1. _ 2_ • Measure voltage drop across B1. • Measure voltage drop across both bulbs in each leg of circuit. _ • Measure amperage through bulbs B1 and B3. • Calculate the total amperage of the circuit. Flow was the answer calculated? • Measure total circuit amperage. • Remove bulb B4 from circuit. • Measure amperage on circuit with only one bulb burning. _ • What is the effect on the total circuit amperage. • What type of circuit is this? Completed circuit should look similar to this. 19 DVOM Circuit 3 Remove all light bulbs and jumpers leaving the power distribution box and switch. Be sure power is off. Build circuit per wiring diagram. DO NOT APPLY POWER AT THIS TIME. • Measure resistance of each resistor at resistor. • Measure resistance between Point 3 on Power Distribution Box (PDB) and Point 2 on Resistor Pack (RP). _ • Are the resistors wired in series or parallel? Resistor Pack Power Distribution Box • Turn on power, measure voltage at power supply. • Turn off power supply. • Using Ohms’ law, calculate the amperage of the circuit at: RP Pin 3._ Hot All Times RP Pin 2. • Turn on power supply and switch. Measure the amperage at: RP Pin 3. _ RP Pin 2 _ • With B- applied at RP Pin3 what is the voltage drop at: RP Pin 3 and PDB? _ RP Pin 2 and PDB? _ • Move B- to RP Pin 2 and re-measure voltage drops. _ • Turn off power supply. Why did the voltage drops differ? _ Mill Mill HIM Mill HIM MIMI Apply B+ here him ij Apply B-here | Mill Jmm Mill HIM |Um HIM ••••I Mill Aft Iftft * 7 " Mill HIM •MM Mill Ml J R ^ k or QX* MMo^_«»-"»*^o| mm mm *ln nnnl » I 1 ,““ HIM HIM Completed circuit should look similar to this. 20 DVOM Circuit 4 Build circuit per wiring diagram. • With power off, Switch in down position mea¬ sure resistance between Point 2 and Com of slide switch. _ Slide switch to up position, measure resistance between Point 1 and Com. _ • Turn on power, put slide switch in up position. • Measure supply voltage at PDB Pins 1/3. • Measure voltage at Pin 86 of relay. • Measure voltage drop between pins 86/85 of relay.(Switch in down position) _ • Check voltage drop between pins 30/87 of relay. • Push down button on push button switch and hold. Recheck voltage drops on relay pins: 86/85. _ 30/87. _ Slide Switch What happened to the voltage drops? • Move red jumper from Pin 2 of slide switch to Pin 1 of slide switch. Put switch in up position. Measure amperage of circuit. _ (Only two bulbs should be burning.) Push button on switch. _ (All lights should burn) Measure amperage. • Continue pushing button, check voltage drop Pin 86 of relay to B- _ What happened? _ Completed circuit should look similar to this. 21 DVOM Review Questions 1. What are the four main factors that determine accuracy of electrical measure¬ ments? 2. What is the importance of impedance in a multimeter? 3. What does a meter reading of OL indicate during Ohms measurement? 4. What is the correct procedure for measuring amps and does this differ from other measurements? 5. Why should test lights be avoided? 6. What happens if the leads are reversed while measuring Ohms of a circuit which includes a diode? _ 7. Why are voltage drop tests preferred over ohms tests? 8. What would a voltage drop of 12.6v across a fuse indicate? 9. What does a voltage drop reading of 12.6v across relay terminals 86 and 85 indi¬ cate? _ What would the expected the voltage drop be across 30 and 87 at the same time? _ 10. When measuring voltage, how is a meter connected to the circuit? _ 22 DVOM